Hydraulic cements, or cements which harden by reacting with water, are most typically illustrated by portland type cements. Portland cement concrete has been known for almost one hundred years and is among one of the most commonly used structural materials. Portland cements are classified into at least five major types according to chemical composition and differing properties resulting therefrom. General purpose portland cements typically contain approximately 60-65% calcium oxide, 20-24% silica, 4-8% aluminum and about 2-5% ferric oxide. Raw material sources for these mineral components include limestone, clay, shale, sandstone, bauxite and iron ore. Mixtures of these raw materials are processed through a kiln fired heat treatment (burning) at approximately 1400.degree.-1600.degree. C. (2500.degree.-2900.degree. F.) to produce a sintered or "clinkered" material, which is then pulverized with 4-5% gypsum to produce the final cement product.
For convenience of further description, the following standard cement industry abbreviations will be utilized to describe the composition of such fired materials:
H--represents water (H.sub.2 O) PA1 C--represents Calcium Oxide (CaO) PA1 A--Aluminum Oxide (Al.sub.2 O.sub.3) PA1 F--represents Ferric Oxide (Fe.sub.2 O.sub.3) PA1 M--represents Magnesium Oxide (MgO) PA1 S--represents Silicon Oxide (Si02) PA1 K--represents Potassium Oxide (K20) PA1 N--represents Sodium Oxide (Na20) PA1 S--represents Sulphur Trioxide (S03) PA1 (1) The amount of sulfate in K.sub.2 SO.sub.4 =0.42 K.sub.2 O PA1 (2) The amount of sulfate in Na.sub.2 SO.sub.4 =0.65 Na.sub.2 O PA1 (3) The amount of C.sub.4 A.sub.3 S=1.995 Al.sub.2 O.sub.3 +1.63 Fe.sub.2 O.sub.3 +1.64 Mn.sub.2 O.sub.3 PA1 (4) The amount of sulfate in C.sub.4 A.sub.3 S=0.26 Al.sub.2 O.sub.3 +0.17 (Fe.sub.2 O.sub.3 +Mn.sub.2 O.sub.3) PA1 (5) The amount of calcium in C.sub.4 A.sub.3 S=0.73 Al.sub.2 O.sub.3 +0.47 (Fe.sub.2 O.sub.3 'Mn.sub.2 O.sub.3) PA1 (6) The amount of CS1.7 [S-(0.65 Na.sub.2 O+0.425 K.sub.2 O+0.26 Al.sub.2 O.sub.3 +0.17 (Fe.sub.2 O.sub.3 +Mn.sub.2 O.sub.3))] PA1 (7) The amount of C in CS=0.41 CS PA1 (8) The amount of C in C.sub.2 S=1.87 S PA1 (9) The total required amount of C=0.55 Al.sub.2 O.sub.3 +0.35 (Fe.sub.2 O.sub.3 +Mn.sub.2 O.sub.3)+1.87 S+0.7 S-0.45 Na.sub.2 O-0.30 K.sub.2 O PA1 (10) The total required amount of S=0.65 Na.sub.2 O+0.425 K.sub.2 O+0.26 Al.sub.2 O.sub.3 +0.17 (Fe.sub.2 O.sub.3 +Mn.sub.2 O.sub.3)
General purpose portland type cement (usually designated ASTM I) typically contains approximately 50% C.sub.3 S, 25% C.sub.2 S, 12% C.sub.3 A, 8% C.sub.4 AF, 5% CS. Thus, the total amount of calcium silicates is approximately 75%, with the predominant silicate being C.sub.3 S. After hydration, such general purpose portland cements generally exhibit compressive strengths on the order of 1800 psi after three days of curing and 2800 psi after seven days of curing, as determined by the standard ASTM procedure C109.
In many forms of concrete construction this rate of strength development for general purpose portland type cement significantly adds to the costs of construction because the cast hydrated concrete must remain supported by forms during a period of time sufficient to allow it to develop adequate strength to permit removal of the forms and to allow additional construction.
Past efforts at overcoming this slow rate of strength development in general purpose portland cement have resulted in the production of high early strength portland cements such as ASTM III which differs from other cements by having higher amounts of C.sub.3 A and/or C.sub.3 S. The minimum ASTM specification for type III portland cement compressive strength is 1800 psi at one day and 2800 psi at three days. However, such cements typically exhibit compressive strengths on the order of 2000-2500 psi at one day and may develop compressive strengths on the order of 5000 psi at seven days.
Nonetheless, there remains a great need to develop cements having much higher early strengths. For example, in the production of pre-cast, pre-stressed, concrete products, a compressive strength on the order of 3000-4000 psi at one day is often required. Additionally, in the construction and repair of highways, many days and even weeks of curing time are required before the highways may be utilized. Moreover, in the construction of concrete buildings and bridges where the cement matrix is cast into forms, it is necessary to allow days of curing time to allow the cement to develop sufficient strength for removal of the forms.
Other hydraulic cements that may or may not be high early strength are the so-called "calcium alumino sulfate" cements based upon 3CaO.3Al.sub.2 O.sub.3.CaSO.sub.4, abbreviated as either C.sub.3 A.sub.3 CS or, preferably, C.sub.4 A.sub.3 S. Typically, the primary characteristic of C.sub.4 A.sub.3 S cements is their expansiveness. Concrete made from portland cement together with sand, gravel, or other mineral aggregate typically undergoes shrinkage upon drying. This shrinkage is undesirable in that, among other reasons, it gives rise to cracks which ultimately weaken the set concrete. Addition of additives such as C.sub.4 A.sub.3 S counteracts this shrinkage and may or may not produce cements having early high strength.
For example, type K portland cement as disclosed in U.S. Pat. No. 3,155,526 (Klein) uses the expansive property upon hydration of C.sub.4 A.sub.3 S in the presence of free C and CS to produce expansive cement components having strengths in the range of standard portland cement. Similarly, U.S. Pat. No. 3,860,433 (Ost et al.) discloses a high early strength cement containing C.sub.4 A.sub.3 S, CS, and C.sub.2 S, which exhibits compressive strengths of at least 2900-4000 psi within 24 hours following hydration.
In spite of these advances in the production of early setting high strength cement, as noted above, the development of portland type cements having even greater compressive strengths and higher rates of strength development than those presently available would be of great economic benefit to the construction industry. Accordingly, it is a particular object of the present invention to provide methods for the production of very early setting, ultrahigh strength cement compositions which following hydration, will produce compressive strengths on the order of 3000-5000 psi within one hour, on the order of 7000 psi within one day.
It is a further object of the present invention to provide methods for the production of very early setting, ultra high strength cement compositions which will produce compressive strengths in excess of 10,000 psi within twenty-eight days following hydration.
It is an additional object of the present invention to provide methods for the production of very early setting, ultra high strength cement compositions which are burned at low temperatures.
It is yet an additional object of the present invention to provide methods for the production of very early setting, ultra high strength cement compositions which beneficially utilize the formation of ettringite crystals to strengthen the hydrated cement.
It is a further additional object of the present invention to provide methods for producing very early setting, ultra high strength cement compositions which are particularly well suited for use in cold temperatures due to their high heats of hydration during their final set.
It is a further additional object of the present invention to provide methods for producing very early setting, ultra high strength cement compositions which achieve very early ultra high strength through the advantageous utilization of combined hydrated ettringite (C.sub.6 AS.sub.3 32H.) and calcium aluminate hydrate (CA.10H).